This invention relates to a system and method for a stand-alone thermostat. In particular, the invention relates to a thermostat that mounts flush to a wall surface and takes in ambient air from the interior of a room. The ambient air is passed by thermal convection across a temperature sensor, thus allowing an accurate measurement of the ambient room temperature.
In office buildings and other occupied spaces which are serviced by heating, ventilating, and air conditioning systems (HVAC), the HVAC equipment is normally controlled by a temperature sensor or thermostat in order to maintain the temperature in the occupied space at a desired level. Typically, the temperature sensor is contained in an enclosure that protrudes into the room from one of its walls. Even though thermostat units that protrude into the room are recognized as architecturally and aesthetically undesirable, such devices have been considered a necessary evil that must be tolerated in order to achieve both good thermal contact with ambient room air and minimal contact with the wall. In the case of wall mounted thermostats, the active temperature sensing element is normally hidden behind a cosmetic cover, which is provided with openings so that room air can migrate behind the cover and come into contact with the temperature sensing element. Measurement accuracy requires that the temperature sensing element have a maximum thermal contact with the air in the conditioned space and minimal thermal contact with the wall and wall space air, which may have a temperature considerably different from that of the ambient room air and thereby introduce significant temperature measurement error.
Several existing art thermostats attempt to address some of the problems of the conventional approach. The thermostat that is subject of U.S. Pat. No. 4,659,236 to Hobbs discloses a flush mounted thermostat. The thermostat of Hobbs includes a cavity with a sensor plate and an insulating block to thermally insulate the sensor plate from the mounting block plate, and integrated circuitry mounted such that heat generated from the circuitry does not interfere with temperature sensing. Hobbs does not include any air circulation system to induce air flows from the room interior across the temperature sensor.
The device of U.S. Pat. No. 5,485,954 to Guy et al. discloses a reduced profile thermostat. The thermostat of Guy et al. includes a cover with a grill opening for free passage of room temperature air into the interior space of the thermostat. It does not include a device for circulating air, such as a heat source, nor does it utilize two sets of openings to facilitate ambient air flow from the room interior across the temperature sensing element.
U.S. Pat. No. 4,347,443 to Whitney discloses a thermostat that uses convective air flow to remove heat generated by electrical components of the thermostat. The device of Whitney includes a circuit board with heat generating electrical components and temperature sensing element mounted toward the front side of the circuit board. The temperature sensing element is thermally shielded from the heat generating electrical components. A passage is provided for convective air flow (xe2x80x9cair washxe2x80x9d) across the back side of the thermostat circuit board to provide cooling of the heat generating electrical components. Temperature differences between room and wall produces an air wash that also traverses a passage containing the temperature sensor.
The thermostat of Whitney does not describe a flush mounted thermostat. Further, Whitney does not rely upon a heat source specifically placed to induce convective air flow across a temperature sensing element, but rather relies on the temperature difference between wall and room to create convection for purposes of air wash across the sensing element.
U.S. Pat. No, 5,381,950 of Aldridge discloses a flush mounted thermostat having a thermostat cover that includes intake louvers that allow ambient air to be drawn across the sensor from the room. The thermostat of Aldridge is either wall mounted or flush mounted and includes two sets of louvers for creating air flow over a temperature sensor, air flow is induced across the temperature sensing element by a fan, and preferably a piezoelectric fan. Aldridge does not include an embodiment directed to convective air flow across the temperature sensing element.
It is an advantage of the present invention to provide a stand-alone thermostat that flush mounts to a wall and includes a sensor exposed to circulating air.
It is a further advantage of the present invention to provide a device for circulating air.
It is further advantage of the present invention to provide a heat source to induce convective air flow across a temperature sensor.
It is a further advantage of the present invention to provide at least two interconnected internal chambers enclosing heat source and temperature sensor elements.
It is a further advantage of the present invention to provide at least one opening for creating air flow over a temperature sensor.
It is a further advantage of the present invention to provide an embodiment including a circuit board containing heat generating and temperature sensing elements, a surface of the circuit board also forming a surface of the internal chambers.
It is a further advantage of the present invention to provide an embodiment having an elastomeric key surface, a back surface of the elastomeric key surface also forming a surface of the internal chambers.
The present invention comprises a stand-alone thermostat that mounts flush to a wall and intakes ambient air from the room interior. A heat generator located near the top of the device causes thermal convection, thus drawing ambient room air across a temperature sensing element. This feature assures that the temperature of room interior air is accurately measured.
To achieve the stated and other advantages of the present invention, as embodied and described below, the invention includes a low-profile thermostat housing, the thermostat housing comprising: at least a first opening enabling ambient air to enter the housing, at least a second opening enabling air to exit the housing; an internal circuit board; an elastomeric key pad comprising a front key surface and a back gasket surface, at least an upper temperature measurement chamber and at least a lower temperature measurement chamber, the temperature measurement chambers defined by the circuit board front surface and the elastomeric key pad back gasket surface, the temperature measurement chambers communicating with the first and second thermostat housing openings by at least two openings that align with the first and second thermostat housing openings, the temperature measurement chambers further communicating with each other via a connecting air passage, and further comprising: a temperature sensing element and a heat generating element, the heat generating element positioned within the upper temperature measurement chamber such that convective air flow is created, the air flow causing ambient air to enter the lower temperature measurement chamber via the first thermostat housing opening, pass over the temperature sensing element, proceed to the upper temperature measurement chamber via an interconnecting air passage, receive heat from the heat generating element, and exit the upper temperature measurement chamber via the second thermostat housing opening.
Additional objects, advantages and novel features of the invention will be set forth in part in the description that follows, and in part will become more apparent to those skilled in the art upon examination of the following detailed description of the invention.